The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus and, more particularly, to an image forming apparatus having a rotary developing device having a plurality of developing sections arranged around the axis of rotation and rotatable about the axis to bring any one of the developing sections to a developing position where an image carrier is located, and a power supply device therefor.
An image forming apparatus of the type described is disclosed in, for example, Japanese Patent Laid-Open Publication No. 61-285468 and includes a power supply device for supplying power to a lamp for sensing toner concentration. The lamp is mounted on a rotary developing device, or revolver, and supplied with power by way of a slidable member positioned at the center of the revolver. The above document also pertains to a method of maintaining a preselected gap between a developing roller and a photoconductive drum by causing the abutment rollers of developing rollers, disposed in the respective developing sections, to get on the drum due to the rotation of the revolver. The document proposes an implementation for preventing, when the abutment rollers hit against the drum, the exposure from becoming irregular at an image writing position and preventing toner on the developing roller from depositing on the drum despite the resulting impact or vibration. Specifically, the apparatus includes first moving means for moving a support supporting the plurality of developing sections, and second moving means for moving the individual developing section relative to the support. Before the developing section at the developing position is replaced with another, it is retracted into the support.
While the power supply device of the above document concentrates on the power supply to the lamp, it is also applicable to other members disposed in the revolver that need power, e.g., developing rollers to which a bias for development should be supplied. However, it is likely that the power supply fails due to the defective contact of the slidable member with the desired member, depending on the configuration of the slidable member. For example, assume that the slidable member is implemented as a conductive brush in order to ensure the power supply against some inaccuracy in the assembly of the revolver and the apparatus body. Then, the brush is apt to collapse and fail to contact the terminal of the other member as the apparatus is operated for a long period of time. On the other hand, when use is made of a rigid terminal free from such deformation, the revolver and apparatus body should be assembled with strict accuracy, resulting in an increase in cost. Moreover, it is likely that the distance between the rigid terminal and the other member changes due to a play between interconnected members and wear attributable to aging, preventing them from contacting accurately.
Furthermore, the mechanism for preventing the developing sections and drum from colliding with each other, as proposed in the above document, has a problem that toner drops from, for example, the developing rollers.